Shane, Thanks for your very helpful (and illuminating) response. No wonder my output is stuttering!
You suggest several solutions – cheapest option seems to be to us Compressor. Do I have to use that on the source clip before I use it or can I use it with the timeline I have already created?
This is probably a one time requirement for me (I usually only use PAL) so I´d like to avoid buying the plug-in if I can!